In general, a compressor as a device for converting mechanical energy into the compression energy of fluid is used for a portion of a refrigeration system such as a refrigerator, an air conditioner, or the like.
The compressor is largely divided into a reciprocating compressor in which a compression space for inhaling or discharging a working gas is formed between a piston and a cylinder such that the piston compresses refrigerant while moving the piston in a linearly reciprocating manner within the cylinder, a rotary compressor in which a compression space for inhaling or discharging a working gas is formed between an eccentrically rotating roller and a cylinder such that the roller compresses refrigerant while being eccentrically rotated along an inner wall of the cylinder, and a scroll compressor in which a compression space for inhaling or discharging a working gas is formed between an orbiting scroll and a fixed scroll such that the orbiting scroll compress refrigerant while being rotated along the fixed scroll.
The reciprocating compressor performs a linearly reciprocating movement on an inner piston within the cylinder to inhale, compress and discharge refrigerant gas. The reciprocating compressor may be divided into a recipro type and a linear type.
The recipro type is a scheme in which a crankshaft is coupled to a rotating motor, and a piston is coupled to the crankshaft to convert a rotational movement of the motor to a linearly reciprocating movement. On the contrary, the linear type is a scheme in which a piston is connected to a mover of a motor performing a linear movement to convert the linear movement of the motor into a reciprocating movement of the piston.
The reciprocating compressor may include a power unit configured to generate a driving force and a compression unit configured to receive the driving force from the power unit to compress fluid. In general, a motor is mostly used for the power unit, and a linear motor is used in case of the linear type.
The linear motor does not require a mechanical conversion device and has an uncomplicated structure since the motor itself directly generates a linear driving force. Furthermore, the linear motor has a characteristic of reducing loss due to energy conversion as well as reducing noise since there is no connecting portion that generates friction and abrasion. Furthermore, when a linear type reciprocating compressor (hereinafter, referred to as a “linear compressor”) is used for an air conditioner, a stroke voltage applied to the linear compressor is changed to change a compression ratio, and thus has an advantage that can be also used for freezing capacity variable control.
On the other hand, for the reciprocating compressor, particularly, linear compressor, the piston collides a cylinder wall or the piston is unable to move forward due to a large load not to properly perform compression when a voltage is abruptly, excessively applied since the piston performs a reciprocating movement while not being mechanically restricted within the cylinder. Accordingly, a control device for controlling the movement of the piston to a load variation or voltage variation is required.
The control device of the linear compressor may be a power conversion device, and perform a power conversion function (for example, AC-DC-AC conversion), thus driving a linear motor through an inverter module.
In general, the power conversion device may include an intelligent power module (IPM), and the intelligent power module (IPM) may be implemented in the form of containing the inverter.
Typically, one intelligent power module (IPM) having three upper arm elements and three lower arm elements may be used to control the U, V and W phases of a 3-phase motor.
However, in case where it is an application field requiring a plurality of refrigeration cycles (for example, when there exist separate refrigeration cycles for a refrigerating chamber and a freezing chamber) or an application field for which a multi-stage refrigeration cycle is used according to an efficient operation or load variation of the compressor, a refrigerator may include a plurality of compressors and a plurality of evaporators.
Accordingly, a plurality of intelligent power modules (IPMs) may be required to drive a plurality of compressors. For example, two intelligent power modules (IPM) may be required to drive two compressors.
As a result, a technology for driving a larger number of compressors through a smaller number of intelligent power modules (IPM) may be required for its simple control and cost reduction.